"Has plan with Sub-S to pay for office expenses"
So, did the Sub S actually pay for those office expense according to that plan?
and ex marks the spot where those rocks and anvils hit me.
Here is how you would do it on a 1040 - Find Business Use of Home (8829) in Deductions > Select 7 (Schedule E (S Corporation)) in the first drop down, then the specific K-1 in the 2nd drop down, then enter all the information for office in home. If depreciation, enter in the depreciation area and link it to this 8829. BUT see #4 at https://amynorthardcpa.com/deduct-home-office-s-corp/