I do not have line of sight to the tower. Is this necessary?

No. Line of sight (LOS) is always desirable but not a critical requirement to establishing good performance. Using a fixed outdoor Poynting antenna improves performance and reliability for 3G/4G LTE even though line of site is not available. Check your service provider’s coverage map, to see if you fall within the coverage area. If you happen to be outside the covered area, often a Poynting antenna solution will still allow for a reliable and stable connection.