In the diagram shown, a blast 3 power would not effect either of the targets there is nowhere to start a blast that would reach them. However, were the character to move up one square they would be able to use the top right corner as the start of the blast and actually effect both targets with no penalty.
There are two reason for this.
The blast would not reach the targets. You have line of effect to the Bugbear, but the blast will not reach him.
If the blast were larger it would reach the Bugbear but not the goblin as there is blocking terrain in the way. I believe the Bugbear would have cover depending on the origin square as one of the line would be blocked.