This makes engagement with infrared homing missiles more difficult because the hot engine exhaust nozzle(s) of the target are pointing away from the attacker.
Typically only all-aspect infra-red homing missiles are able to perform head-on engagements.
Radar-guided missiles are typically able, however head-on many aircraft have a much smaller radar cross-section so the radar may not be able to track/lock onto the target at maximum range in this type of engagement[dubious – discuss].
Missiles typically have a lower chance of hitting a target in a head-on engagement because of the very fast closure rate.
It has the advantage, however, of greatly increasing the effective range at which missiles or cannons can be used.