it's my fault. instead of immediate base capture troops has to "hold it" for some time. when time is comes and too much troops are died (or all of them died) - capture is failed. but insertion is successful - you did your job.
insertion missions will be really interesting when there is will be some enemy infantries fighting back. you insert troops under heavy fire, taking off and flying around the base shooting from side machine gun. but now it's quite boring.