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no, the thing that controls when compression begins is the closing of the intake valve. The longer you delay this, at low rpm, the more time there is for the piston, which is now on the way up on the compression stroke, to push a portion of the Just inducted air/fuel charge, back up into the intake. This is what creates the low engine vacuum signal at idle, in the intake.

Maybe this will help. Here are all the durations of the Five parts of a 4-stroke engine cycle;
overlap, intake, compression, power, exhaust, and back to overlap. If you have a 268/276 cam, you already know the durations of two of those, ie 268 and 276.
But you need to know the LSA of that cam, to calculate the other three.
Let's say it's on a 114 Lsa. The overlap is calculated from averaging the intake and exhaust durations and subtracting from that, double the LSA. Ok then, the calculation looks like this
(268 +276)/2 less (2 x 114) = 44* overlap.

The compression degrees is what is leftover after you add a portion of the overlap, to 360 degrees which is half of the 4-stroke cycle. How much overlap to add depends on where you installed the cam centerline. Lets say we install it 4* advanced , therefore 114 less 4= 110. so the Formula looks like
360 plus (268/2 less 110); less 268 = compression degrees; so
360 +24 less 268= 116* of compression

the Power cycle is 360 plus whatever overlap is left, less the exhaust duration. Since we started with 44* overlap and gave 24* to the intake/compression half, we have 20* overlap left over, so
360 +20, less 276 = Power = 104*

Ok so, lets line them up in their proper order and make sure it adds up to (2 x360) plus 44 =764 which is the complete 5-stroke cycle.
268 intake, +116 comp +104 Power +276 Exh =764, so Good to go. The 44* overlap is buried in the 268 plus 276.

Ok so lets tighten up the LSA to 106* and see what happens;
First up is calculating the overlap, which was the average of intake plus exhaust, less double the LSA, and that looks like
(268 +276)/2 less (2 x106)= 60* overlap. Lets install this at split overlap giving 30* each to intake and exhaust. Therefore, to get compression,
360 +30, less 268 =122 compression. and
to get Power we add 30 to 360, and subtract the exhaust duration, like this
360+30, less 276= 114 Power, and lining them up we get
268 intake +122 comp +114 power +276 exhaust =780, and subtracting 720 for 2 full crank revolutions, we get 60* overlap, exactly as previously calculated, so we know the math is correct.
Now lets compare the 114 LSA to the 106 LSA;
268 intake +116 comp +104 Power +276 exhaust (the 114)
268 intake +122 comp +114 power +276 exhaust (the 106)
notice this trick gave us
an extra 6 degrees of compression, and
an extra 10 degrees of power extraction, for a total of 16 *
How'd that happen?
Well, it's in the overlap, which climbed from 44* to 60*, which is the same 16 degrees.
Finally, 122* of compression is usually better than 116, unless it leads to detonation. and
114 Power extraction can be better than 104, depending on what the car is being used for. At just 104* this engine is gonna be thirstier for fuel than at 114.
So, if hiway fuel economy is important, then 114 is better.
But absolute Power might be higher at 104.
However, I installed this cam at split overlap, so it could be retimed either way depending on what you need, say up to 4* retard to 6 or even 8 degrees advanced. Thus you trade compression for Power extraction, or vice-versa.
Hope that helps