Join in progress as an option not for somebody to invite a friend , friends play with friends , an option to join for random players matches should be there and there are tons of posts In their forum about this . I totally understand life reasons and I agree with you , I ' m a parent with young kids and things happen and you need to shut everything off , but because of life reasons , they should respect the other player too as their time is valuable too specially in wave 42 after 40 minutes of playing , add a new player immediately , exactly as other games do it , fill the gap with another player that just started a match , for join in progress players they should receive the normalaverage xp that was give from wave 1 until the wave that they joined but the xp or rewards cannot be cashed until wave 50 , then that player will receive full score points , rewards and more after 50 is done , he never missed on anything joining later .