TLV-EWR and TLV-SFO are among the best markets for United. Rarely you can spot R space available, however, sometimes, you can find R in the TLV-EWR and TLV-SFO during holidays (e.g. I can see now Tuesday, October 10th). Your chance of clearing into R space is flying during mid-week (Tuesday-Wednesday), booking UA85 and not UA91 (which is mostly soldout) and the best way is to find how many P fare buckets are available. For example, if you spot P6-P9 two weeks before the flight, most likely your upgrade will be cleared. Also, booking Q,U instead of W will increase your chance.