Academy of Secrets: Suggestions for increasing module difficulty [spoilers likely]

[zjs]

I'm planning to run Academy of Secrets as a one- or two-shot for a party of three 13th level PCs. The players all typically make powerful (but not broken) characters, so I like to make sure I'm prepared to adjust the power level of modules before I run them.

Normally, running a group at the printed level with one fewer characters is at least a good start for a handicap, but at least for Part Two, it seems like being down a PC is actually an advantage. Modifying NPCs/monsters by bumping HP or applying the "Advanced" template are always quick-and-dirty options, but I'd prefer plan some more interesting modifications and only use those if the planned changes are insufficient.

Has anyone run the module at a higher difficulty (or thought about how they might)?

[Mark Moreland]

Since many of the foes in the adventure are devils, one option would be to simply replace them with higher CR devils and shake up the backstory a bit to accomodate the different devils' roles within Belzeragna. I find that a creature created for a given CR is generally a little bit more challenging than a creature advanced through simple templates to the same CR, simply because its special attacks and overall concept often handles higher-level PC tactics better.

[Banesfinger]

Actually, I was wondering if the adventure is too difficult:

The initial Breaching festival is a CR 11-13 encounter.

Exploring the Hall of Wards could have (optionally) up to three extra encounters: CR 13, 14, and 14.
The last two (manditory) areas are the Arena (CR 13) and the Calling Hall (CR 15).
As stated (pg 14) it is possible to "rest" in the Hall due to the Flowing Time - but this may be unlikely due to the small size of the Hall, or if the PCs don't completely understand the flowing time...

Regardless of resting, immediatly after the Calling Hall encounter, the PCs have four encounters in rapid succession (CR 12, 12, 13, 13) and a possible conflict with Toff (CR 16).

This means the group could have 11 encounters in a row (two of which are challenging, one Hard, and the final one Epic)! This seems a little deadly to me...?