Dave
The question isn't in the slightest ambiguous.
What you've now concluded is that, on a high pressure day (QNH = 1024mb), an aeroplane at an aerodrome located 968ft above sea level will perform as if it were actually at 1,598ft above sea level.
There's nothing ambiguous about that, it's just plain wrong! Oh, and another thing, by concluding that the aeroplane is 1,598ft above the 1013mb pressure level, you're saying that it's
1,928ft above sea level (1,598 + 30x(1024-1013))!
Pressure altitude is what the altimeter will read when the subscale is set to 1013mb, nothing more, nothing less and no possibility for two sets of answers. You had already worked out yourself that there was no way the altimeter would read 1,598ft at aerodrome level on that day when set to 1013. You correctly concluded it would read 630ft. So what do you now think the 1,598ft means?
Believe it if you want to, but it is dangerously wrong thinking and I would strongly advise you to seek out some seriously better informed opinions before you ever try performance-limited take-offs from hot and high airfields.
It's worth noting that if the QFE is higher than the standard setting of 1013, then a subtraction will be used at the end.
You'd have to wait a long time at that airfield for those conditions ... it would need a sea level pressure >1045mb!!!!!!!