The part of the sentence "a slightly more difficult" is correct and can be used in written English.
It is generally used to describe something that is more challenging than the norm. For example, "This test is a slightly more difficult than the last one, so make sure you study hard."
Why is this a slightly more difficult game? Let's keep the mikes handy a second.
A slightly more difficult trend to spot is that of cleanliness.
But finding a pair of jeans that fits right is a slightly more difficult undertaking.
My mind, too, has become nicely obedient to correct "non-winning thought", which is a slightly more difficult and complex thing.
And while the previous biennale's theme, "Wonder," favored aesthetically pleasing and more accessible works, this year's biennale is taking a slightly more difficult conceptual tack.
Argentina (95), for instance, appear to have only a slightly more difficult task than England (104), yet Jose Pekerman's team have to play Holland, a fate Eriksson was relieved to avoid, and the potentially tricky Ivory Coast.
Unless you're toting a butane oil filled vape, sneaking fat zoots into a club is slightly more difficult than sliding a pinger in the recesses of a sort of hidden jacket pocket.
In recent years, Trump, the man, has tried to distance himself from Trump, the casinos, a task made slightly more difficult by the fact that his name appears in neon on the buildings.
In the model presented, the definitions of the genetic and phenotypic variances in a given environment are slightly more difficult than in the standard reaction norm models because a non-linear function of random correlated variables is involved.
With a friend, is it slightly more difficult?
Under the lights at Arthur Ashe Stadium, in a match that was slightly more difficult than expected, Federer defeated Simon Greul of Germany, 6-3, 7-5, 7-5.
