I think because this is still uncharted territory somewhat, "unsettled science', makes perfect sense every doctor is going to have their own subjective risk tolerance.
A patient should match their own risk tolerance with a doctor who's similar. End of honestly.
Far as the underside I could see maybe the areas on either side of the urethra , but not beneath it, being lower risk.
There aren't a ton of studies analyzing filler for dicks to begin with, nevermind any showing specifically what happens to the underside. They exist, sure, but compare that to the number normally required to reach a medical consensus and we're still in VERY uncharted territory.
As for doctors i would expect the responses to range from "the risk is minimal" to "the risk is exceptional" but anyone tell you there's no risk...not buying it.
Likewise if a doc says "we can go ever so slightly on the underside, and do, but we won't cross over beneath the urethra as there's a risk of stricture", that would be a sensible answer to me. As would an answer of "even on either side of the urethra the risk of stricture is unacceptably high for us" - which, again, i think given how few studies, there is no consensus truth, only individual doctors' logic and intuition. These are the best we're going to be able to do until there are a gazillion studies specifically on ventral filler.
I personally wouldn't do it unless the doc said there was a portion he specifically wanted to avoid, because I can absolutely see the theoretical risk Dr C points out.