Is that true though? Are you saying this because it has a "tactical mode", or because you've looked at the source code? Because the source code is out. The tactical option is named "tactischeModus" and appears
1. NMP:
Computes a slightly different NMP factor for this mode. Namely,
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(540 + 66 * ((unsigned int)diepte / PLY) // <-- Tactical
(480 + 76 * ((unsigned int)diepte / PLY) // <-- Non Tactical
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if (slagOfPromotie || geeftSchaak || pos.vooruitgeschoven_pion(zet))
verlenging = PLY;
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&& (!Threads.tactischeModus || diepte < 12 * PLY || st->ply > 3))
So, no, Houdini is not special for its tactics. It has a Trivial tune of NMP, a root node extension that mostly only happens in test positions, a LMR condition which is seen and used by a dozen "tactical" SF forks, and that blob 4, which does reduced depth searches on varying aspiration windows. 4) is the sole contribution that Houdart made to search.
Houdini is an unimpressive fork of Stockfish. __unimpressive__. Half the users on this form have come up with better search tweaks for tactical positions than are present in this code base. I suspect Fire is just the same, as Norman was not even smart enough to adjust the values of the tables he copy pasted from Stockfish (Piece-Square Tables, Storm Danger tables, Half-density Bit Mask Thread Scheduling Tables, ....)