Ohh My, the rabbit warren of things here.
1) Ambient Temperatures will affect the swelling factor. Generally not very much - so this is a minor issue.
2) Charge & Discharge rate does affect internal cell temps due to the chemical interactions.
3) Expansion & Contraction is normal BUT it is not supposed to be excessive, the general allowance is 0.5mm to a max of 1.0mm (See Manfacturer Spec Sheet for particular cell type.
Compression VS Fixing. I will not do the 20 runs around the Mulberry Bush (which already has a terribly deep moat as a result. So in simple point form.
1) Ambient Temp should be between 20-25C (68-77F)
2) Cell SOC should be between 3.000-3.200 Volts per cell. NO Higher than 3.200 ! (THAT is the Nominal Mid-Point of the Voltage Curve (50% SOC).
3) They do NOT need to be squeezed ! A MAXIMUM is 12psi but 10psi (Pounds per Square Inch) is more than sufficient. That is hand-squeeze tight.
SPECIAL NOTES:
* NEVER EVER SQUEEZE OR FORCE CELLS ! Seams can pop as can pressure valves which means the cell is Junked !
NB: The Aluminium used for LFP cells is barely thicker than a soda pop can, keep that in mind !
** IF cells have expanded, discharge cells below 3.200 volts, even to 3.000, apply GENTLE pressure slowly and allow to sit for 2-4 hours (No Charging or discharging), then if still excessively bulged, you can squeeze again (GENTLY) and allow to sit a few more hours... Use a hard flat surface on the face (piece of plywood or similar) so that pressure is even across the faces of the cell. An Entire pack can be compressed in this fashion.
-> FYI / LESSON-LEARNED Dept: It is far simpler to Bind Cells into 4-Cell "Blocks/Modules" and then assemble your pack in 4,8,16 cell configurations as required. If for any reason you need to extract cells it's easier to pull out a 4-pc block and more manageable. Remember that 280AH Cells for example weigh 5kg/11lbs each, which can become unmanageable pretty quickly.
WARNING !
KISS explanation. Think of the contents in the cells like one long rectangular jelly roll with many many very thin layers (like flaky pastry thin). This makes putting pressure on them tricky as it has to be even across the surface. If one spot get's more pressure too fast it can weaken the material and spacing between the layers ultimately leading to a failure. Please do NOT "ManHandle" or force the cells, be gentle and polite.
Closing Note:
It is extremely RARE to see perfectly square/flush FLP Cells, it is just how they are made & assembled. There will always be a slight "wave" in the casings depending on temps & SOC etc... Even ABS Cased LFP like Winston or SinoPoly will "undulate" but less noticeable due to case design but it still occurs. They also recommend Binding/Fixing with MILD Compression.
THAT'S THE RUB: Folks are hung up on the term "Compression" leaping to the assumption that "force" is required, when only Mild Binding - Securing is what is being called for. This is all THANKS TO TRANSLATION SOFTWARE and how things are interpreted.
Hope it helps, Good Luck.