I am currently dedicating some study time to constructing check/raising ranges in SRPs out of the BB after we cold called pre. In general, one of the best guidelines I have heard so far is: Raise polar vs. a polar c-bet and raise merged vs. a merged c-bet. This makes a lot of sense to me except for situations in which the flop heavily favors the PFR range. I'm unsure about how we approach such a situation.

Let me elaborate. Suppose we're playing BU vs. BB in a heads-up SRP and we checked to the PFR.

Flop: 874ss
This is a board where the PFR will check back quite some hands and c-bet polar for at least 1/2 potsize. Our check/raising range is polar and our value part is constructed around sets, straights and top two. Against a polar range, medium strength hands (like 7x, 4x) have no incentive to raise and fold out the PFR's bluffs while isolating themselves vs. the value range.

Flop: K74r
Very nice range c-bet board for the PFR. The K interconnects well with the top part of the BU's range while this part is missing in the BB's cold calling range and increases the BU's pre-flop range advantage. The dryness of the flop provides little equalization potential for the BB to catch up. BU will c-bet range here, and BB reacts with a merged check/raising range for a high frequency. For instance, our 4x and 7x are incentivized to deny equity against all the broadways and overcards that are still part of the PFR's unfiltered pre-flop range and can even get some value from the BU's Ace high-calldowns.

Flop: AJ4r
This is where my confusion sets in. The BU is going to range c-bet this board for the same reasons as elaborated above. Using the rule of thumb to raise merged with a high frequency vs. a merged c-bet, we would raise hands like 4x for equity denial vs. overcards. The problem is that the the flop is crushing the PFR's opening range so hard that the BB basically doesn't have any value hands apart from maybe 44 (and some occasional AJo). If we don't really have a value component to construct our raising range around, what do we do here?

1. Do we go polar again and raise AJ/44 to go with backdoors?
2. Do we stay with the rule of thumb and raise merged, but for a significantly lower frequency than on the K74r flop?
3. Do we avoid having a raising range at all and play call-only?

Any thoughts welcome...