Tend to second that observation. I have toyed with a few changes for Foxhole/Trench effects during some homemade scenario designs (mostly PTO). Dependent on the situation or the side a couple of approaches are:
- Units in Foxholes [EX: Spider Holes or well camouflaged positions] in concealment terrain to lose concealment as Guns when firing. This approach seemed to work well as an SSR for engagements in especially rough terrain or with/against troops of vastly differing experience levels in jungle warfare.
- Allow units in Trenches (mostly) in concealment terrain to gain concealment as if the unit were behind Bocage. (This I think worked quite well even in German vs Russian engagements where a side had sufficient time & resources to dig in over an extended period of time [EX: Kursk, The Little Land, or even 1944 AGC at the outset of Bagration]).
I have yet to see such an SSR in a published scenario that I have played but I expect someone will come along sooner or later and publish something in a fairly similar in approach. One thing I have noticed with this approach is that attacker to defender ratios must be increased more toward realistic odds to achieve the same goals as without such an SSR and that the game moves along a bit faster because there is less unnecessary movement (skulking) during turns.