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

for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    
    aa=max(a)
    
    if len(set(a))==1:
        print(-1)
    else:
        for i in range(n):
            if a[i]==aa:
                if i==0:
                    if a[1]<a[0]:
                        print(1)
                        break
                elif i==n-1:
                    if a[n-2]<a[n-1]:
                        print(n)
                        break
                else:
                    if a[i]==a[i+1] and a[i]==a[i-1]:
                        pass
                    else:
                        print(i+1)
                        break