So the top of the roof is in compression and collar ties near the upper roof should also be in compression not in tension.
Removing roof collar ties.
You might actually need 2x8 rafters in such a case.
Well unless your roof is concrete tile and less than 3 12 in slope.
It ties the entire roof together.
The only time collar ties do any good is when they are specifically designed to be functional by an engineer or architect and are installed with meticulous care by the framer according to detailed drawings.
Collar ties are generally for the benefit of the rafters though and your rafters sound more than big enough.
An exception occurs however even near the ridge if the bottom of the roof triangle is not secured against stretching or flattening by a ceiling joist or a low placed rafter tie.
The one in the middle is around 3ft height which results in an awkward limbo or high jump.
Watch this video before.
There is 3 supports on the loft which i believe are either called rafter or collar ties which divide the loft into quarters.
Collar ties are the appendix of roof framing an evolutionary dead end in home building hanging on by just a couple of nail points.