Signing on EOS/Senior MDES scheme

Hey redditors! I am very interested working in the military sector and I like the regimental life of it. I am seeking to know is there any way to sign on EOS / Senior MDES schemes in the RSAF as a diploma holder. I have completed my BMT but did not get send to OCS. Basically, I have contacted the recruitment centre and they told me that I have met the basic requirements for EOS but they rejected my application outcome without disclosing the reasons.

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If I were to go for University and get a degree to improve my chances, and maybe they can still reject me without me knowing. Some background about me is that I have a business diploma in a polytechnic and my GPA is around 2.9+. I do not currently have a University placement yet. Hopefully can make the cut for SUSS/SIT though. Apart from EOS, I would also like to know if it is possible to apply for Senior MDES after completing a degree, or with a university placement while still serving my NS obligation and possibly progress towards OCS. Any advice would be appreciated, thank you!

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Ps, I do not really have a particular vocation that I really like in mind, maybe because I am not studying engineering/computer related courses so I do not have much knowledge for the Senior MDES vocations. However, I am keen on signing on except the EWOS or junior MDES schemes. Thanks again!