If I may, this is more of a Halacha l×maaseh question on this Inyan.
People are fixing the placement of their tefillin shel rosh that it should be bein einecha
Throughout the entire davening. Is that halachically mandatory or does one adequately perform the mitzvah of tefillin if at a minimum the shel rosh is in its proper place during krias shema?
Thank you
Bezalel
Every moment that one wears Tefilin properly is a Mitzva of the Tora, and a major one at that. Tefilin that are not in their proper place are the same as Tefilin that are in their embroidered bag. It is a shame to wear Tefilin for 45 minutes and have only 5 minutes of mitzva, no? I would ask a different question: Why should someone need to adjust his Tefilin all the time? There is probably a simple solution to this problem, for example: 1) have the straps adjusted for a better fit (by someone with the Halachic knowledge to do it properly)2) a haircut at closer intervals 3) find one of the Halacha Seforim with detailed pictures or diagrams of the proper place for Tefilin; there is a bit of play in the correct positioning and a more informed state may lead to less "in flight corrections" 4) if the adjustments are done without a Tefilin mirror, the use of a mirror may reduce the number of adjustments necessary.
In general. We don't answer "Halacha LeMaaseh" questions, but I see this more as a practical issue than a halachic issue. I hope this was a satisfactory answer to your question. If not please be back in touch.
Shimon Brodie