"I doubt that logic applies if you buy additional shares after...

"I doubt that logic applies if you buy additional shares after accepting the offer though - there are various clauses in the offer booklet saying (in effect) that increases in your holding don't count. For example, in Section 9.1 (e)."

I must admit that I haven't read the offer proposal, only the synopsis provided by Leighton on their website (I will read Hochtief's Section 9.1(e) tomorrow, but it is 11:30PM in Perth now and I am whacked). I am basing my opinion on this statement:

"If you do not accept the Offer and instead sell some or all of your Leighton shares on-market, they will trade "cum-Offer" on a normal settlement basis, and a purchaser of those shares may accept the Offer."

http://www.leighton.com.au/investor-and-media-centre/hochtief-offer

The need for a separate LEI and an LEIE ticker only makes sense (at least to me) on the basis that they have different entitlements. So the fact that LEI is trading $20+ and LEIE has offers around the $15+ mark (no trading yet) is because those who buy LEI can sell 3/8 at $22.50 to Hochtief, but those who hold LEIE cannot. I may be wrong, but that is how I read it.