1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

try:
    t=int(input())
    while t:
        t=-1
        n=int(input())
        a=list(map(int,input().split()))
        if len(set(a))==1:
            print(-1)
        else:
            mx=max(a)
            for i in range(n):
                if a[i]==mx:
                    
                    if i>0:
                        if a[i-1] <mx:
                            ans=i+1
                            break
                    if i <n-1:
                        if a[i+1] <mx:
                            ans=i+1
                            break
            print(ans)  
except:
    pass