Oh boy, the smallest light I used a de-domed emitter in was a C8, but got about 100 kcd with it, so doubled the kcd - it's a XM-L2 U2/SinkPAD running at 3.85A I believe. I haven't noticed any issues like that in the beams of all the de-domed lights I did, quite a few now. My biggest is my TN31 which is doing 347 kcd - pretty sick for under $10 in parts, posting in this thread: https://budgetlightforum.com/t/-/17637.
I'm thinking the XM-L2's de-dome easier/better - pretty much all my de-domes, accept the very first, are XM-L2's.