Order of the (Tower) Shield

It struck me that, since you share your mount's space when in mounted combat, if you used a tower shield to provide cover it'd cover a 10ft section of map (for a medium character on a large mount) rather than just a 5ft section. Rather than magically growing the shield's size, I'd imagine this as using the mobility and height advantage of being mounted to swing the thing around more, covering a larger area.

Assuming this is true (which is RAW as far as I can tell, but I imagine some GMs would ban-hammer, but still...), then being mounted with a tower shield and using the Shield Wall Feat would seem to provide a nice big defensive screen for your allies with the Shield Wall Feat (since they also benefit from your tower shield's one-way cover).

This naturally led to a Cavalier build, as a Cavalier can both ignore the hideous ACP to Ride checks for hefting a tower shield about, and can use the Tactician class feature to grant his allies (mount included) the benefits of the Shield Wall Feat.

Here's what I've got so far...

... so he's basically a tanky type, although like all tower shield users he's always got the option to stow the thing and go in swinging two-handed. You still threaten when using a tower shield for cover, so when mounted and claiming cover he can leverage the lance being a one-handed reach weapon to potentially AoO several enemies (hence the Combat Reflexes) if they try to bypass him and reach his charges (being the other PCs, one imagines). He'll need the Mounted Combat Feats and the other basics as he levels, of course, but this sets up the concept at level 1.

So... any thoughts, suggestions, improvements? Any gaping holes I'm missing?

I suggest you read Shield Wall before proceeding further...

Yeah, shield wall doesn't quite do what you think it does.

It requires you allies to have the feat (though as a cavalier you could grant it to them) and to actually wield a shield.

Further, your tower shield isn't 10ft wide nor does it provide cover to your mount. Actually, using a tower shield while mounted works out to be fairly s&!+ty since you occupy all squares your mount does, but can only provide cover to one 5ft edge of those squares.

Even if it did cover 10ft, it still requires your allies to have the feat, be adjacent, and be wielding a shield.

You only need to be wielding a shield to gain the AC bonus from Shield Wall, the tower shield cover part doesn't state that it requires a shield.

Shield Wall (Combat, Teamwork)

You form a unified defense with those around you.

Prerequisite: Shield Proficiency.
Benefit: Whenever you are wielding a shield and are adjacent to an ally wielding a shield who also has this feat, the AC bonus from your shield increases, depending on the shield wielded by your ally. If your ally is wielding a buckler or a light shield, your shield bonus increases by +1. If your ally is wielding a heavy shield or a tower shield, your shield bonus increases by +2. You keep these bonuses even if your ally loses his shield bonus due to making a shield bash attack. If an adjacent ally with this feat uses a tower shield to grant total cover, you also benefit if an attack targeting you passes through the edge of the shield (Core Rulebook 153).

You share your mount's space when using mounted combat.

A horse (not a pony) is a Large creature and thus takes up a space 10 feet (2 squares) across. For simplicity, assume that you share your mount's space during combat.

A tower shield used for cover blocks one side of your space, not a map square.

Shield, Tower: This massive wooden shield is nearly as tall as you are. In most situations, it provides the indicated shield bonus to your AC. As a standard action, however, you can use a tower shield to grant you total cover until the beginning of your next turn. When using a tower shield in this way, you must choose one edge of your space. That edge is treated as a solid wall for attacks targeting you only. You gain total cover for attacks that pass through this edge and no cover for attacks that do not pass through this edge (see Combat). The shield does not, however, provide cover against targeted spells; a spellcaster can cast a spell on you by targeting the shield you are holding. You cannot bash with a tower shield, nor can you use your shield hand for anything else.

So now we've all read the relevant rules text, any helpful build comments? :)

The helpful comment I would have is that I think many people are not going to agree with your interpretation of things, just as I don't.

While it might be a very literal reading of RAW, many people care more about the intent of the rules rather than the letter.

Expect variation.

Which is fine... but I didn't post this in the Rules Questions thread for a reason! ;)