[Chrisbee]

Before you give on that low bass try other listening positions (if at all possible).
Moving your chair or sofa backwards or forwards can effect the bass response dramatically.

Did you have your SPL meter near your normal ear level when seated? It matters in my room and might also in yours.

For the small amount of money involved it might be worth investing in another SPL meter to confirm you have the correct compensation. Just because the case looks like an RS meter doesn't mean it has exactly the same roll-off.

The lower bass response curve measured by REW (or any other software) depends critically on the roll-off curve of the meter itself. If you haven't matched the meter with the correct compensation curve you can't say for sure that the meter is reading correctly. Your missing bass could just be a figment of your meter's imagination. Or, it might just be perfectly compensated and your bass really is rolling off early.

The nearer you are to your sub the better as far as bass levels are concerned. If moving your listening chair backwards or forwards doesn't do it for you then the option remains to move the sub physically nearer your chair.

REW is so quick to take tests that you can try half a dozen positions in a few minutes. Think flexibly about your seating position and your sub's position to see if the curve flattens out to your advantage. You don't have to move your chair yet. Just keep moving the SPL meter a few inches then test and retest until you find the best spot.