Leuntnant or Lnt.d.Res

[saxon lions]

What determined when a German soldier was eventually promoted from the ranks during WWI whether he became a Leutnant in the Regular Army or in the Reserve or indeed the Landwehr. I have numerous examples of both Georg Weiner in the Regular Army, and Rudolf Windisch in the Reserve but do not know how this was determined. I know it was a big deal when Max Immelmann a Lnt.d.Res was promoted to Oblt in the regular Army as a reward for his feats, and i believe there were significant benefits to a Regular Army commission.