That ratio is not absolute truth.
Correct. There is no "magic ratio" (even though it *seems* to make sense). Rather, with any guiding routine written in the past 20+ years, what you need is a guide system that can adequately sample the guide star and generate a reliable sub-pixel centroid. That's it. If your guide scope was capable of keeping your mount on target with the old imaging train, it should be capable of doing so with the new OTA.
In other words, the imaging tube is independent and just along for the ride on a, presumably, well-guided mount.
Now, a different but related issue is that some users have lower resolution imaging rigs which are less sensitive to some guiding issues. If they buy bigger imaging OTAs then the OTA/camera is not only heavier (often with longer moment arms) such that it stresses the mount more, but it also captures the mounts tracking errors with higher fidelity. In that case, the mount was never guiding well - the user just happens to notice it more after the upgrade.
If it were me, I'd leave it alone and see how it does.