No, nothing to do with signal strength - we talk about manual tuning so as to eliminate multiple transmitters which can confuse the EPG data and result in lost recordings. Of course, being digital the image quality will always be fantastic (especially on Hidef) until you get no image at all.
Blocking the OTA update search is about preserving a known firmware rather than allowing a newer (possibly buggy) firmware to be installed. In particular, 1.02.20 does not allow automatic retunes - and retunes destroy your recording schedule. Any more recent firmware retunes behind your back. All the background to this is in "Things Every HD/HDR-FOX Owner Should Know" (link in my signature panel at the bottom of this post).
You have not mentioned your recording settings - are you on AR or padding? If AR then try padding. The reliability of AR will depend on which services you are in the habit of recording. It may be coincidental, but my AR became much more reliable after my box went through a factory reset (Menu >> Settings >> Installation >> Factory Default) - but beware that this will return it to the unconfigured state requiring a retune and full setting up (it does not delete your existing recordings).