The insurance issue is not length of delay, but whether no show for a separate ticket is a delay at all.

Many US policies cover these delays and have a very specific definition of "trip" which includes the transfer between tickets when the time is above MCT had the two tickets been booked as one. Thus, had OP booked KL-UA via LHR and the scheduled time at LHR was above the MCT, he could also collect on such a policy.

I would also point out that AA, as a OW member with a substantial presence at LHR, has a unique contractual provision not specifically applicable to this OP, but perhaps other travelers. AA "protects" across AA-AA and AA-OW tickets. Thus, in the reverse direction separate tickets might not be a risk if the second ticket was to OW.