New to options so bear with me. In a calendar trade if you want to do a directional trade say long . If you buy a call 60 days out and sell call 21 days out . If the 21 day call you sold expires does the 60 day buy call just continues as a straight buy call with no restrictions on profits since the sell call expired ?
IMO, you are looking at it backwards. You need to have an expectation of what the stock will or won't do over a time period. Then determine what spread works best to profit from that assumption with the given option prices. After that, a balance of risk/reward and margin useage would be something you can create your own rules for.
model out the prob distribution of the stock and pick the best strike(s) to reflect your forecast... for example... there are bullish patterns (maybe bollinger band breakout) and there are BULLISH patterns (bollinger breakout+ ACD+stock mired in a 52 week low that breaks out of channel on huge volume,etc) so adjust your strike(s) to reflect that....
also watch out for the volatility crush on upmoves (at least in US equities..) so you may want to have an idea of the iv hi/lo range of the tickers ur trading.