First of all, REM doesn’t always improve the HAs’ performance from their initial gain prescription. If the HAs perform up to snuff to begin with and don’t underperform, and/or if the fitting selection and ear canal shape are the ideal choices and ideal conditions as to not drag down the HA’s prescribed performance further, then the clinician will see that the initial prescribed gain curves already matching well against the target gain curves, and therefore no further adjustment is needed. From this point of view, you can walk into a REM session and walk out of it with the exact same result you came in with no improvement, because nothing needs to be adjusted/improved. In this case, REM does not equal “better”. In this case, REM equals “verified to be up to snuff against the target already, no further adjustment needed.”
Now it’s not clear how REM was done in your case. If it was done by an external standalone REM setup, then most likely REM will be performed against a standard fitting rationale, probably NAL-NL2. This is because the mfg’s proprietary fitting rationales is private (a trade secret) and the external REM machine can only work with standard/publicly know rationales.
If the mfg’s programming software (in this case, Phonak Target for you as a Phonak user) can accommodate and support a number of REM equipments, and allow its Target software to work well with these REM equipments, then the Phonak APD proprietary fitting rationales can be calculated by the software target to be APD-based, because this Target software has the knowledge to calculate using APD rationales, while the external REM software doesn’t.
So let’s say you had REM done with an external/stand-alone REM hardware/software setup, then most likely it’s set to the standard rationale NAL-NL2 as the target. Even if the original prescription was the Phonak proprietary-based APD rationale, the clinician has now adjusted to “force fit” it into the target NAL-NL2 standard already.
The standard rationales may not work wonder for everybody. Some who have always used it and are used to its characteristics may prefer it to mfg proprietary rationales. Apparently for you, your ears don’t like the standard rationales for certain reasons. It seems like your ears like the Phonak APD rationale better. So that can explain why you found the REM adjusted result (to NAL-NL2) not as good as the proprietary APD rationale that was most likely used in the “quick fit”.
Even let’s say that you have “virgin ears” and have not been exposed to either rationales, so they couldn’t possibly have a preconceived notion to favor one over the other, remember that standard rationales don’t know much about the hearing aids per se, and therefore a lot of assumptions had to be made about how the hearing aids work in order for the developers to arrive at a more “universal” rationales that got adopted as standard.
On the other hand, the HA mfg who developed their own proprietary rationale specifically made for their own HA brand has intimate knowledge of how their own HAs work, and therefore no assumptions had to be made about how their HAs work (unlike the assumptions that had to be made in the development of the standard rationales). So it’s possible that the HA mfg’s proprietary rationales used in the “quick fit” simply just work better for their brand of HAs compared to the standard rationale that might have been forced fit to your HAs when REM was done. And the proprietary rationale may work better because they fit their own HA’s brand better like a glove.