That is odd. The recording and live are the same tuners. The only thing I can think of is something in the tivo circuitry making the record signal slightly stronger then the live, but that maybe normal. We are talking about the 4 tuner roamio, right? I don't have a roamio, but have premiers on cable and a series 3 hd on an indoor antenna that works great. Both models have a feature where you can check each individual tv channel for signal strength for antenna aiming. I would think roamio would have the same feature somewhere in the menus. On mine it's msg. & settings>settings>channels>signal strength-antenna. My tivo has a 0 to 100 range. 0 to 50 I get nothing at all. 51 to 56 it gets pixed with audio drop outs. 57 and up, no problem. It seems like you might be in that very small 51 to 56 range. If you can't find antenna strength on your tivo, it could be you inadvertently set it for cable on initial set up.
3- Premier XLs,
2- HD Series 3 w/1tb expansions,
5- TiVo "N" adaptors,