I was reading your post then realised it started well over a year ago. The only thing that came to my mind that another member alluded is the secondary mirror size. Moving 100mm up the tube means the secondary is intercepting a larger light cone. This would normally require a larger secondary to ensure there is sufficient illumination from centre to edge of field and that you at least get some 100% illumination in the centre. If the secondary was oversized you may be ok but if undersized then you are probably not getting the full use of the primary now both visually and photographically unless you increase the secondary size.
If it were me I would at least do the calcs to see where I stand but probably would not do anything about it as the difference may not be detectable or minimal and not be of concern. However the typical backfocus for a DSLR is approx 50mm and the fact that you had to move 100mm could indicate you had a smaller secondary because that is all was needed which is a good thing for visual as it improves contrast.
So basically you accept an illumination drop off and potentially zero 100% illumination in the centre or increase the secondary size. As to which is better would depend on just how much magnitude loss you are getting and if increasing the secondary then just how much contrast will be affected by the larger secondary. To determine contrast factor divide sec. minor axis by primary diameter, eg. 2.14” sec/10” primary =21.4% contrast factor (good is around 20% up to 25%). Better is (15-20%). Most SCTs are 30-40% albeit with less contrast (planets most noticeable visually). Don’t sweat over it because if your over 25% and are getting great views it’s probably having a good quality primary and secondary mirror (all else equal) than any affects of contrast from an oversized secondary.
If your getting illumination drop off too but have good quality primary and secondary giving you great images with great contrast then that’s fine too, it’s just not optimised fully to give full use of the primary.
You can do the calcs at
https://www.bbastrodesigns.com/diagonal.htm
If you have trouble with the online calcs, sing out.