Since it's a moving target (troops are added every week) the problem would keep repeating itself. I would think the threshold should be set to a certain distance from the total number of troops, rather than a static number
for example, if there are currently 331 troops in the game (not counting GW troops, as no one can have them to mythic yet), the threshold can be set to 20 away from that (so 311) and 25 for honorable mention (so 306). Then on monday, when 3 new troops are added, the threshold would automatically become 314, and 309 for honorable mention.
It doesn't have to be those numbers of course, but the general idea, whatever numbers you decide.