Not sure I understand you. You can take more of the loss if you have other regular account sales that have a gain.
The Roth conversion is not a gain or loss, it is just a distribution and taxed as ordinary income tax. In retirement accounts like 401K and IRA you don’t consider buys or sells, gains or losses.
You do not report sales, interest, dividends,gains, losses or any transactions inside the IRA or 401K accounts. You only report distributions, Rollovers, Transfers, conversions that you get a 1099R for. That's one of the benefits of using an IRA or 401K Account. It grows tax deferred. Then when you take it out you pay ordinary income tax on it. But you don't get the lower capital gains tax on it.
If you have a loss you will just have less income to take out of it, so less tax to pay.
