Reasoning:

If you have many groups, to iterate though all takes very long (even with the new groups <side>) - for perFrame execution filtering per SQF is very expensive.

nearGroups would look for any unit within the radius - not just the leader, and would add that group to the return.

Suggested format:

_groups = position/object nearGroups distance;
_groups = position/object nearGroups [side,distance];
_groups = position/object nearGroups [[sides],distance];

Return Value: Array of Groups - not sorted

It should also exclude non simulated groups.